
NSF Org: |
AGS Division of Atmospheric and Geospace Sciences |
Recipient: |
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Initial Amendment Date: | August 27, 2019 |
Latest Amendment Date: | October 29, 2019 |
Award Number: | 1933056 |
Award Instrument: | Standard Grant |
Program Manager: |
Roman Makarevich
AGS Division of Atmospheric and Geospace Sciences GEO Directorate for Geosciences |
Start Date: | October 1, 2019 |
End Date: | September 30, 2023 (Estimated) |
Total Intended Award Amount: | $899,997.00 |
Total Awarded Amount to Date: | $899,997.00 |
Funds Obligated to Date: |
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History of Investigator: |
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Recipient Sponsored Research Office: |
800 WEST CAMPBELL RD. RICHARDSON TX US 75080-3021 (972)883-2313 |
Sponsor Congressional District: |
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Primary Place of Performance: |
800 W. Campbell Rd Richardson TX US 75080-3021 |
Primary Place of
Performance Congressional District: |
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Unique Entity Identifier (UEI): |
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Parent UEI: |
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NSF Program(s): |
AERONOMY, Upper Atmospheric Facilities |
Primary Program Source: |
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Program Reference Code(s): |
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Program Element Code(s): |
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Award Agency Code: | 4900 |
Fund Agency Code: | 4900 |
Assistance Listing Number(s): | 47.050 |
ABSTRACT
This project supported by the Geospace Facility's Distributed Arrays of Small Instruments (DASI) is to provide the operations and maintenance of the Low-Latitude Ionospheric Sensor Network (LISN). This distributed array is spread across South American and measures dynamics of the ionosphere. This is synergistic with other Geospace Facility's investments in South America such as Jicamarca Radio Observatory. It provides important geographic coverage. Examination of the ionosphere is called out in several of the benchmark recommendations in the 2015 National Space Weather Action Plan. Monitoring of the ionosphere as daily weather is monitored on the surface of Earth is important because radio communications can be significantly impacted by ionospheric activity.
This project to operate LISN distributed observatory for the three years will allow detailed observations and investigations of the origin, dynamics, coupling, and mapping of traveling ionospheric disturbances (TIDs) and the formation and evolution of plasma irregularities in the low- and mid-latitude ionospheres to be carried out. LISN contains Global Positioning System and Global Navigation Satellite System receivers for determining total electron content and ionosondes for measuring TIDs. These simultaneous measurements may provide insight into how multi-scale TIDs at low latitudes seed plasma phenomena, such as equatorial plasma bubbles, at mid latitudes. The complexity of the plasma dynamics requires multiple perspectives on the natural system. This award also supports an upgrade to the servers and data products for public dissemination.
This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
PUBLICATIONS PRODUCED AS A RESULT OF THIS RESEARCH
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PROJECT OUTCOMES REPORT
Disclaimer
This Project Outcomes Report for the General Public is displayed verbatim as submitted by the Principal Investigator (PI) for this award. Any opinions, findings, and conclusions or recommendations expressed in this Report are those of the PI and do not necessarily reflect the views of the National Science Foundation; NSF has not approved or endorsed its content.
The NSF funding allowed the operation of the Low-latitude Ionospheric Sensor Network (LISN) distributed observatory for four years. A distributed observatory consists of several low-cost instruments that function continuously and provide real-time variables of the ionosphere. Typically, they extend across regions encompassing thousands of km. In our case, the LISN instruments probed the whole South American continent. LISN includes GNSS receivers, magnetometers, and small radars called ionosondes that measure the density profiles of the ionosphere. Recently, oblique-sounding receivers have been added to the LISN network.
One of the main objectives of the grant was to understand the onset of irregularities in the low-latitude ionosphere during extreme inputs from below (stratosphere) and from above (magnetosphere). We have examined the effect of Sudden Stratospheric Warming (SSW) events produced at the polar stratosphere on the equatorial ionization anomaly, bubble production, and scintillations. This study reported that on February 12, 2016, several networks of GPS receivers observed enhancements of L-band scintillations (Figure 1). During this day, TEC maps exhibited a large-scale (thousands of kilometers) almost-circular structure within the equatorial ionization anomaly during the nighttime hours (Figure 2). The anomaly redistribution and scintillation enhancements were found to be related to the onset of a minor SSW event. Figure 1 shows a sequence of total electron content (TEC) perturbation values originated by the transit of several equatorial plasma bubbles (EPB). The effect of EPBs is to produce negative excursions of the perturbations. The TEC depletions on the left frame and the corresponding scintillations on the right are indicated with an arrow pointing to the EPB observation time. Figures 1b-1g show the L-band scintillation measured by six GPS receivers. On February 12, 2016, we found an unusual scintillation increase at 02:10 UT, almost two hours after the TEC depletions formed and when TEC depletions/EPBs were transiting near central Brazil. The first station to observe a significant scintillation level associated with the TEC depletion reported S4 ~0.2. Thirty minutes later, the scintillation peak becomes 0.3. And 90 min later, when the EPB passes through Alta Floresta, the S4 index increases to ~0.6. The largest scintillation value is observed at Santarem, where scintillations reach a value > 1.2.
Figure 2 shows the initiation of a dramatic morphological change of the equatorial anomaly during the SSW event of February 2016, in which a north-south aligned segment develops near the center of the South American continent, joining the north and south crests of the EIA. On the western side of South America, the southern crest of the anomaly fades, and its amplitude falls below 20 TEC units. This plasma behavior can be explained by a trans-equatorial meridional wind moving the plasma along the field lines, transporting plasma from the northern crests toward the magnetic equator and into the southern hemisphere. This investigation concluded that wind shears and reversals near 60° W help increase scintillations. It was also emphasized that the role of SSW events must be included in any empirical and numerical model of scintillations and spread F.
The grant’s funding also allowed us to examine the condition when near one kilometer (N1K) irregularities originate at the low latitudes ionosphere. We used ground-based measurements that are part of the LISN network to realize that N1K irregularities are created when the pre-reversal enhancement of the vertical drift is unusually intense and long-lasting. In addition, a strong southward wind along the field lines prevails at low latitudes during the appearance of N1K irregularities. Under these circumstances, the bottomside F region is lifted above 550 km, creating a region extending in altitude and longitude where the equatorial ionosphere is highly unstable and able to amplify any seed irregularity. The left frame of Figure 3 shows an N1K event where the C/NOFS satellite recorded near sinusoidal fluctuations that reached values close to 30% of the background ionosphere density. The high altitude of the F layer (center panel of Figure 3) implies a cooling of the plasma that produces a negative Ti gradient in the F layer. It is suggested that a negative Ti gradient, collocated with a positive density gradient at the F-region bottom side, can initiate the ion temperature gradient instability (TGI). This instability creates 1-kilometer seeds for the Rayleigh-Taylor instability that amplifies. It was also observed that N1K irregularities generate frequency spread ionograms, as depicted in the right frame of Figure 3.
Last Modified: 12/31/2023
Modified by: Cesar E Valladares
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